pkgコマンドでspdylayを入れたらtmuxが削除された

$ sudo pkg install spdylay
 Updating FreeBSD repository catalogue...
 FreeBSD repository is up-to-date.
 All repositories are up-to-date.
 The following 2 packages will be affected (of 0 checked):

New packages to be INSTALLED:
	spdylay: 1.2.5_1
	libevent2: 2.0.21_2

The process will require 2 MB more space.
426 KB to be downloaded.

Proceed with this action? [y/N]: y
Fetching spdylay-1.2.5_1.txz: 100%  172 KB 176.4k/s    00:01
Fetching libevent2-2.0.21_2.txz: 100%  254 KB 259.8k/s    00:01
Checking integrity... done (1 conflicting)
Checking integrity... done (0 conflicting)
Conflicts with the existing packages have been found.
One more solver iteration is needed to resolve them.
The following 5 packages will be affected (of 0 checked):

Installed packages to be REMOVED:
	tmux-1.9.a_1
	libmemcached-1.0.7_2
	libevent-1.4.14b_3

New packages to be INSTALLED:
	libevent2: 2.0.21_2
	spdylay: 1.2.5_1

The operation will free 3 MB.

Proceed with this action? [y/N]: y
[1/5] Deleting libevent-1.4.14b_3: 100%
[2/5] Deleting tmux-1.9.a_1: 100%
[3/5] Deleting libmemcached-1.0.7_2: 100%
[4/5] Installing libevent2-2.0.21_2: 100%
[5/5] Installing spdylay-1.2.5_1: 100%